Recording liquid, printed product and ink jet recording method

ABSTRACT

A recording liquid characterized in that when it is printed with 100% duty and with a resolution of 600x300 dpi on an electrophotographic paper having a S.A.D (Surface Area Difference) of from 6.0 to 9.0 and a pH of from 6 to 8, the S.A.D. of the printed portion is at least 59.5.

The present invention relates to a recording liquid employing an aqueousmedium. Particularly, it relates to a recording liquid for writing orink jet printing, especially a recording liquid suitable for ink jetprinting.

Heretofore, a water-color ink containing an acid dye or a direct dyedissolved in an aqueous medium, or a solvent-type ink containing anoil-soluble dye dissolved in an organic solvent, has been used as arecording liquid for ink jet printing. The solvent type ink contains asolvent and thus has a problem from the viewpoint of environmentalsafety, and it is not suitable for use in offices. On the other hand,the water-color ink containing a water-soluble dye, has a problem thatthe record will be poor in water resistance, when recording is made on apulp paper. The record with the ink also has a poor light resistance.The same problems are also found in the recording liquid for writing.

To solve such problems, it has been proposed to use an aqueousdispersion ink employing a water-insoluble pigment with excellent waterresistance and light resistance as a coloring material. However, withthe conventional aqueous dispersion ink of a water-insoluble pigment,its storage stability and the recording density of the record wereinadequate, and it was difficult to satisfy the properties of the recordsuch as improvement of the printing density, prevention of printingirregularities, etc. and the properties of the recording liquid such asthe storage stability, the jetting stability, etc., at the same time.Accordingly, further improvements have been desired.

It is an object of the present invention to provide an aqueousdispersion ink which, even when recorded on pulp paper or regeneratedpaper by writing or ink jet recording, gives a record with a highdensity and good printing quality and which is excellent in the storagestability and the jetting durability, whereby a record excellent also infastness such as light resistance or water resistance, can be obtained.

As a result of various studies for improving the printing density of anaqueous dispersion black ink employing a water-insoluble pigment, thepresent inventors have found that the S.A.D. (Surface Area Difference)of a printed portion when a recording liquid is solid-printed on a pulppaper, interrelates to and gives a substantial influence to both thestorage stability of the recording liquid and the printingirregularities, and recording density of the printed product. Thepresent invention has been accomplished on the basis of this discovery.By the present invention, it will be possible to obtain a recordingliquid which is capable of satisfying the high printing density of therecord and the storage stability and jetting stability of the recordingliquid, at the same time.

That is, the present invention provides a recording liquid characterizedin that when it is printed with 100% duty and with a resolution of600×300 dpi on an electrophotographic paper having a S.A.D (Surface AreaDifference) of from 6.0 to 9.0 and a pH of from 6 to 8, the S.A.D. ofthe printed portion is at least 59.5.

In short, the present invention defined the recording liquid in terms ofthe S.A.D. of the printed portion which is in the specific range.Whereas, with conventional ink jet recording liquids, the S.A.D. valuesas defined by the present invention are at a level of about 59.2 atbest.

Now, the present invention will be described in detail with reference tothe preferred embodiments.

The S.A.D. (Surface Area Difference) as defined by the presentinvention, represents the specific surface area of a record and is aparameter defined by the following formula. In the present invention,the following conditions are to be employed for its measurement.

S.A.D (Surface Area Difference)={(ΣSi/ΣPi)−1}×100 (%)

where Si is the area of every triangle formed by adjacent three datapoints, Pi is the area when Si is projected to a xy plane, ΣSi is thesum of all Si, and ΣPi is the sum of all Pi.

Measuring Method

Apparatus: Scanning Probe Microscope

Type of Machine: NanoScope III, manufactured by Digital InstrumentsCompany

Scanner: J-Head

Measured Region: 1 μm×1 μm

Number of Pixels: 512×512

Scan Rate: 1.5 Hz

Measuring Mode: Tapping AFM

Probe: Si-DF 20, manufactured by Seiko Instruments Company

Image Treatment: Planefit Auto Tertiary

In the present invention, printing is carried out with 100% duty andwith a resolution of 600×300 dpi on an electrophotographic paper, suchas 4024 paper (manufactured by Xerox Corporation) having a S.A.D. withina range of from 6.0 to 9.0 and a pH within a range of from 6 to 8 asmeasured by a cool water extraction method as described in JIS P8133,and the surface of the printed portion is measured under the abovedescribed measuring conditions to determine the S.A.D. The measuredregions are portions other than fiber portions of the paper, and anaverage of four points (four regions) is taken as the data. Theabove-mentioned 4024 paper is an electrophotographic paper containing arosin-type abietic acid as a sizing agent and from 1.8 to 2.2 wt % of Tiatoms in the paper.

As described above, with the recording liquid of the present invention,the S.A.D. of the printed portion is at least 59.5. However, with a viewto improvement of the recording density, it is preferably at least 60.0,more preferably at least 62.0, most preferably at least 65.0. But, inconsideration of smear, the S.A.D. is preferably at most 90.0, morepreferably at most 85.0, further preferably at most 80.0, mostpreferably at most 70.0. Namely, in consideration of the overallperformance of the recording liquid, it can not be said that the higherthe S.A.D. value, the better, and it is advisable that the S.A.D. valueis within the above-mentioned specific range. The present invention isbased on the discovery of the optimum range for the S.A.D.

Further, it has been found that when the recording liquid of the presentinvention is used, it is possible to accomplish high density printing ofsuch a level that the density OD of the printed portion is at least 1.5as measured by means of a Macbeth reflection densitometer (RD914).

The recording liquid of the present invention has good storage stabilityas compared with conventional recording liquids and has a characteristicsuch that the change in the particle size distribution of the recordingliquid is small even when stored at a high temperature for a long periodof time. Specifically, it is possible to present a recording liquidwhereby, when the particle size distribution measured immediately afterthe preparation of the recording liquid is compared with the particlesize distribution measured after storing the recording liquid for oneweek at 70° C., to take differences for the respective fractions of themeasured particle sizes, the total of such differences is at most 20%,preferably within a range of from 1 to 18%, more preferably from 2 to15%. If this total value is too small, flocculation on a recording sheetwhen recorded, tends to be poor, whereby the printing density tends tobe low, or printing irregularities tends to result, such beingundesirable.

In the present invention, the method for calculating the total ofdifferences between the particle size distribution immediately after thepreparation of the recording liquid and the particle size distributionafter storage of the recording liquid for one week at 70° C., is asfollows.

{circle around (1)} Measurement of the particle size distributionimmediately after the preparation of the recording liquid

Firstly, the recording liquid immediately after the preparation, is usedat the concentration as it is, and measurements are carried out by aparticle size distribution meter (MicrotracUPA, sold by Nikkiso) underthe following conditions.

Measuring Conditions (Input Parameters)

Transparent Particles: No, Spherical Particles: No,

Particle Refractive Index: 1.81

Particle Density: 1.86

Fluid Refractive Index: 1.33

High Temp: 30.0° C., Viscosity: 0.797 cP

Low Temp: 20.0° C., Viscosity: 1.002 cP

Run Time: 300 (sec), Number of Runs: 2

An average value of two measurements conducted under the above measuringconditions, is taken as the value for the particle size distribution ofthe recording liquid.

{circle around (2)} Measurement of the particle size distribution of therecording liquid after storage for one week at 70° C.

The recording liquid is stored for one week at 70° C., and after thestorage, it is returned to room temperature, and at the concentration asit is, the particle size distribution is measured by the same method asin the above item {circle around (1)} by a particle size distributionmeter (MicrotracUPA, sold by Nikkiso), and an average value of twomeasurements, is taken as the value for the particle size distributionof the recording liquid.

The results obtained in item {circle around (2)} are compared with theresults obtained in item {circle around (1)}, and differences are takenfor the respective fractions of the measured particle sizes, and theirtotal is calculated.

The reason as to why the recording liquid in the present inventionprovides the above-mentioned superior performance is not clearlyunderstood, but may be explained as follows. When the recording liquidof the present invention is recorded on a recording material (a papersheet or a film), the water-insoluble pigment contained therein readilyundergoes flocculation, whereby the S.A.D. of the surface of the printedportion becomes to be at least 59.5, and thus a high recording densitycan be realized. While the recording liquid of the present inventionundergoes flocculation on a recording material, it undergoes noflocculation during the storage of the recording liquid, andaccordingly, a stabilized record can always be obtained. Conventionalrecording liquids did not have such apparently opposite properties atappropriate levels. In the field of coating materials, it has been takenfor granted that the printing density is high when the surface of theprinted portion is smooth i.e. the S.A.D. is small. Thus, it has beenunexpected that the printed density becomes high when the S.A.D. of thesurface of the printed portion is large, as in the present invention.Thus, the present invention is based on a discovery of the fact which isunexpected from the common knowledge of the prior art.

In the present invention, the characteristic of the recording liquid isdefined by using as an index the S.A.D. (Surface Area Difference) of theprinted portion, when printing has been carried out with 100% duty witha resolution of 600×300 dpi on an electrophotographic paper having aS.A.D. (Surface Area Difference) within a range of from 6.0 to 9.0 and apH within a range of from 6 to 8. However, so long as the recordingliquid satisfies such a definition, printing may be carried out on anyrecording sheet. For example, when the recording liquid of the presentinvention is employed for an ink jet recording method, the recordingsheet may, for example, be a pulp paper such as an electrophotographicpaper (such as Xerox 4024, Xerox 4200, Canon PB, Canon LC-301, CanonCP-250 or Epson KA4250NP), a regenerated paper (such as Xerox Green100or Xerox R), a coated paper (such as Canon HR-101s, Lexmark 1402650,Lexmark 1402781, or HP 51634Z), a glossy paper (such as Canon GP-201,Canon GP-101, Canon HG-101, Canon HG-201, Canon BF-102, Canon BF-102,Canon KH-201, Epson MJA4SP6, Epson MJSP5, Lexmark 1402796, Lexmark1372361, Lexmark 1372208, HP C6043A, or HP C5984A) or an OHP film (suchas Canon CF-102, Epson MJOHPS1N, Lexmark 1402798, or HP C3835A).

To the recording liquid of the present invention, various additives maybe incorporated. For example, a dispersant may be incorporated. Usefuldispersants are not particularly limited and include, for example,various anion surfactants, nonionic surfactants, cationic surfactants,amphoteric surfactants and polymer type dispersants.

The anionic surfactants include, for example, fatty acid salts, alkylsulfates, alkylbenzene sulfonates, alkylnaphthalene sulfonates,alkylsulfosuccinates, alkyldiphenylether disulfonates, alkyl phosphates,polyoxyethylenealkyl sulfates, polyoxyethylenealkylaryl sulfates, alkanesulfonates, naphthalene sulfonic acid-formalin condensates,polyoxyethylene alkylphosphates, and α-olefin sulfonates.

The nonionic surfactants include, for example, polyoxyethylenealkylethers, polyoxyethylenealkylaryl ethers, polyoxyethylene derivatives,oxyethylene/oxypropylene block copolymers, sorbitane fatty acid esters,polyoxyethylene sorbitol fatty acid esters, glycerol fatty acid esters,polyoxyethylene fatty acid esters, and polyoxyethylene alkylamines.

The cationic surfactants and amphoteric surfactants include, forexample, alkylamine salts, quaternary ammonium salts, alkyl betaines andaminoxides.

The polymer type dispersants include, for example, poly(meth)acrylicacids, (α-methyl)styrene/(meth)acrylic acid copolymers,(α-methyl)styrene/(meth)acrylic acid/(meth)acrylate copolymers,(α-methyl)styrene/maleic acid copolymers, (α-methyl)styrene/maleicacid/(meth)acrylate copolymers, (α-methyl)styrene/methacrylic acidcopolymers, (α-methyl)styrene/methacrylic acid/acrylate copolymers,(α-methyl)styrene/maleic acid half ester copolymers, α-olefin/allylether/maleic acid copolymers, (α-methyl)styrene/(α-methyl)styrenesulfonic acid copolymers, vinylnaphthalene/maleic acid copolymers,vinylnaphthalene/(meth)acrylic acid copolymers or their salts (such asalkali metal salts of e.g. lithium, sodium and potassium, or organicamine salts of e.g. triethanol amine, monoethanol amine, and2-amino-2-propylalcohol). Here, (meth)acrylic acid means acrylic acidand/or methacrylic acid, and (a-methyl)styrene means styrene and/orα-methyl styrene. Among them, a polymer which serves as a dispersant anda binder for improving the smear property, is preferably employed.Especially from the viewpoint of the smear resistance of the record, itis preferred to add a polymer such as a block polymer, a graft polymeror a random polymer. From the viewpoint of the production cost, a graftpolymer or a random polymer is preferred, and particularly preferred isa random polymer. The weight average molecular weight of such a polymeris preferably at most 50,000, more preferably at most 15,000, from theviewpoint of the jetting stability of the resulting recording liquid.

In the present invention, as a binder, an anionic polymer, a nonionicpolymer, an amphoteric (betaine type) polymer, a cationic polymer or aresin emulsion may, for example, be incorporated.

Among these polymers, anionic polymers having anionic water-solublegroups selected from carboxylic (carboxylate) groups, sulfonic(sulfonate) groups and phosphoric (phosphate) groups, are preferablyemployed. However, a polymer having hydrophobic groups, or a polymerhaving anionic water-soluble groups having a pKa of at most 3, isfurther preferred from the viewpoint of the storage stability andjetting stability. Among them, a polymer having carboxylic (carboxylate)groups or sulfonic (sulfonate) groups, is most preferred from theviewpoint of the discharge stability and dispersibility, andparticularly preferred is a polymer having sulfonic (sulfonate) groups.

As hydrophobic groups in the anionic polymer, a functional group havingan aromatic ring, such as a phenyl group, a benzyl group or a naphtylgroup, or a linear or branched alkyl, alkenyl or alkinyl group having atleast 4 carbon atoms, which may be substituted, may, for example, bementioned.

Specifically, the anionic polymer to be used in the present invention,may, for example, be a styrene/acrylic acid copolymer, a styrene/acrylicacid/acrylate copolymer, a styrene/maleic acid copolymer, astyrene/maleic acid/acrylate copolymer, a styrene/methacrylic acidcopolymer, a styrene/methacrylic acid/acrylate copolymer, astyrene/maleic acid half ester copolymer, a styrene/styrene sulfonic(sulfonate) copolymer, a vinyl naphthalene/maleic acid copolymer, avinyl naphthalene/acrylic acid copolymer, a naphthalene sulfonicacid-formalin condensate, a lignin sulfonic acid, or a salt thereof.Among them, a styrene/acrylic acid copolymer, a styrene/acrylicacid/acrylate copolymer, a styrene/maleic acid copolymer, astyrene/maleic acid/acrylate copolymer, a styrene/methacrylic acidcopolymer, a styrene/methacrylic acid/acrylate copolymer, astyrene/maleic acid half ester copolymer, or a styrene/styrene sulfonic(sulfonate) copolymer, is further preferred. Further, in order to obtaina printed product which has a good color tone and which does not runwith water, such an anionic polymer is preferably not colored.Accordingly, preferred is one whereby the maximum value of theabsorbance within a range of from 380 to 780 nm, is at most 0.05g⁻¹·I·cm⁻¹, particularly at most 0.01 g⁻¹·I·cm⁻¹.

To the recording liquid of the present invention, other additives suchas a surface tension controlling agent or an antiseptic may further beincorporated.

In the present invention, the above-mentioned anionic polymer and theabove-mentioned nonionic additive may be employed in combination. Insuch a case, the ratio in content of the anionic polymer and thenonionic additive is preferably from 12:1 to 1:1, more preferably from10:1 to 2:1, from the viewpoint of the storage stability and theprinting density.

The water-insoluble pigment to be used in the present invention may, forexample, be an organic pigment, an inorganic pigment, a disperse dye oran oil-soluble pigment. Specifically, the following may mentioned.

Specific examples of a pigment to be used for an yellow ink, includeC.I. pigment yellow 1, 2, 3, 12, 13, 14, 16, 17, 73, 74, 75, 83, 93, 95,97, 98, 114, 128, 129, 151 and 154.

Further, specific examples of a pigment to be used for a magenta ink,include C.I. pigment red 5, 7, 12, 48(Ca), 48(Mn), 57(Ca), 57:1, 112,123, 168, 184 and 202. Specific examples of a pigment to be used for acyan ink, include C.I. pigment blue 1, 2, 3, 15:3, 15:34, 16, 22 and 60,C.I. bat blue 4 and 60. Other than the above, C.I. pigment red 209, 122,224, 177 and 194, C.I. bat violet 43, C.I. bat violet 3, C.I. pigmentviolet 19, 23 and 37, C.I. pigment green 36, 7, or C.I. pigment plue15:6 or 209, may also be used.

The oil-soluble pigment may, for example, be C.I. solvent yellow 16, 21,25, 29, 33, 56, 82, 88, 89, 150, 151 or 163, C.I. solvent red 24 or 27,C.I. solvent blue 14, 25, 38, 48, 67, 68, 70 or 132, C.I. solvent black3, 5, 7, 27, 28, 29 or 34. Other than the above, oil yellow 105 or 107,balifast yellow 1101 or 1105, balifast red 1306, balifast blue 1603,1607 or 2610, balifast black 1802, 1807 or 3830 (the foregoing,manufactured by Orient Kagaku Kogyo K.K.), aizenspiron yellow GRLH or3RH, aizenspiron blue GNH, 2BNH or BPNH, aizenspiron black MH or GMH(the foregoing, manufactured by Hodogaya Chemical Co., Ltd.), oleosolblue G, oleosol black AR (the foregoing, manufactured by Taoka KagakuKogyo K.K.), or orasol black RL1 (manufactured by Chiba Gaigy) may, forexample, be mentioned. The disperse dye may, for example, be C.I.disperse yellow 3, 82 or 54, C.I. disperse red 60 or 191, or C.I.disperse violet 57.

Further, in the present invention, a carbon black such as acetyleneblack, channel black or furnace black may be employed. Among them,furnace black is preferred. The carbon black to be used, usually has aDBP oil absorption within a range of from 60 to 300 ml/100 g, preferablyfrom 90 to 200 ml/100 g, from the viewpoint of the recording density,particularly preferably at least 140 ml/100 g. Further, the 24M4DBP oilabsorption is preferably at least 80 ml/100 g, particularly preferablyat least 90 ml/100 g. Further, the volatile content is usually within arange of at most 8 wt %, preferably at most 4 wt %, more preferably atmost 3 wt %. In addition, the BET specific surface area is preferably atleast 150 m²/g from the viewpoint of the storage stability and dischargestability, particularly preferably within a range of from 200 to 1,000m²/g. The primary particle size is preferably at most 40 nm from theviewpoint of the storage stability, more preferably at most 20 nm,further preferably at most 16 nm, most preferably at most 13 nm.Further, its pH is preferably from 2 to 10, particularly preferably from6 to 9. Here, the DBP oil absorption of carbon black is a value measuredby method A of JIS K6221, the volatile content is a value measured bythe method of JIS K6221, the BET specific surface area is a valuemeasured by method D of ASTM D3037, the pH is a value measured inaccordance with JIS K6221, the 24M4DBP oil absorption is a valuemeasured by the method of ASTM D3493, and the primary particle size isan arithmetic average diameter by an electron microscope.

Specifically, such carbon black may, for example, be #2600, #2300, #990,#980, #960, #950, #900, #850, #750, #650, MCF-88, MA-600, #95, #55, #52,#47, #45, #45L, #44, #40, #33, #32, #30, #25, #20, #10 or #5 (theforegoing, manufactured by Mitsubishi Chemical Corporation), Color BlackFW1, FW2, FW2V, FW18, FW200, Special Black4, 4A, 5, 6, 100, 250, 350,550, S160, S170, Printex U.V.140U, 140V, 95, 90, 85, 80, 75, 45, 40, P,60, 300, 30, 35, 25, 200, A, G, 6, L (the foregoing, manufactured byDegussa), Regal415R, 330R, 1250R, 995R, Monarch800, 880, 900, 460, 280or 120 (the foregoing, manufactured by Cabot), Raven 850, 780ULTRA,760ULTRA, 790ULTRA, 520, 500, 410, 420, 430, 450, 460, 890 or 1020 (theforegoing, manufactured by Columbia).

In the present invention, among the above described water-insolublepigments, a carbon black is particularly preferred.

The water-insoluble pigment to be used for the recording liquid of thepresent invention may be one having a water-insoluble pigment chemicallytreated (such as oxidation treatment or fluorination treatment) or onehaving a dispersant, a surfactant, etc., physically or chemically bonded(e.g. by graft treatment, or one having a dispersant preliminarilyadsorbed prior to dispersion), so long as it is one having the abovephysical properties. The aqueous medium to be used for the recordingliquid of the present invention comprises water as the main componentand is preferably one having a water-soluble organic solvent added towater. The water-soluble organic solvent may, for example, be ethyleneglycol, propylene glycol, butylene glycol, diethylene glycol,triethylene glycol, polyethylene glycol (#200 or #400), glycerol, analkyl ether of such a glycol, N-methylpyrrolidone,1,3-dimethylimidazolinone, thiodiglycol, 2-pyrrolidone, sulforan,dimethylsulfoxide, diethanolamine, triethanolamine, methanol, ethanol orisopropanol.

The recording liquid of the present invention may contain in addition tothe above described components, a water-soluble resin, a fungicide, adisinfectant, a pH-controlling agent or urea, as the case requires.

The recording liquid of the present invention may be prepared in such amanner that the above-mentioned respective components are mixed, and thewater-insoluble pigment is pulverized into fine particles and dispersedby means of a dispersing machine. The dispersing machine may, forexample, be a jet mill such as a nanomizer or an ultimizer wherebypulverization can be carried out without employing a medium, as well asa ball mill, a roll mill or a sand grind mill. Particularly preferred isa sand grind mill or a jet mill free from contamination derived from amedium.

After the pulverization and dispersion, coarse particles are removed bymeans of a filtration machine or a centrifugal separator. Componentsother than the water-insoluble pigment, the dispersant and water, may beadded after the pulverization and dispersion treatment. Thepulverization and dispersion treatment can be effectively carried out bypreparing the liquid at a high concentration. Accordingly, it ispreferred that a treated liquid prepared at a high concentration isfinally diluted with an aqueous medium to adjust the concentration ofthe recording liquid.

It is preferred to adjust the average particle size of thewater-insoluble pigment in the recording liquid within a range of from0.01 to 0.4 μm from the viewpoint of the dispersion stability and thejetting stability. The average particle size is more preferably from0.01 to 0.3 μm, most preferably from 0.1 to 0.3 μm. Further, the maximumparticle size of the water-insoluble pigment is at most 5 μm, from theviewpoint of the dispersion stability and the jetting stability.

The composition of the recording liquid is not particularly limited, butin order to obtain a record wherein the S.A.D. of the printed portion isat most 59.5 as defined by the present invention, such can beaccomplished by optimizing the type of the water-insoluble pigment andthe blend proportion of the dispersant.

The amount of the water-insoluble pigment is usually within a range offrom 1 to 20 wt %, based on the total weight of the recording liquid,preferably from 3 to 15 wt %, more preferably from 5 to 15 wt %. Theamount of the dispersant is usually within a range of from 2 to 100 wt%, based on the weight of the water-insoluble pigment, preferably from 3to 50 wt %, more preferably from 5 to 20 wt %, most preferably from 5 to15 wt %.

The amount of the water-soluble organic solvent in the recording liquidis usually within a range of from 5 to 30 wt %, preferably from 10 to 20wt %. The amount of a polymer which serves as a dispersant and/or asmear resistance-improving agent, is preferably within a range of from0.1 to 5 wt %, more preferably from 0.2 to 3 wt %.

The object of the present invention can readily be accomplished by arecording liquid prepared especially in such a manner that as thewater-insoluble pigment, one having a DBP oil absorption of at least 140ml/100 g is selected, and dispersant is incorporated in an amount offrom 5 to 15 wt %, based on the carbon black.

More preferably, in such a recording liquid, a carbon black having aprimary particle size of at most 20 nm is used. Particularly preferably,a carbon black having a BET specific surface area of from 200 to 1,000m²/g or a volatile content of at most 4%, is employed. Further, anexcellent recording liquid can be obtained by selectively using a carbonblack having preferred physical properties, as mentioned above withrespect to the carbon black.

With respect to the water-insoluble pigment, the dispersant, theadditive and the organic solvent, a single type of substance may beemployed alone, but, in some cases, two or more different types ofsubstances may be used in combination, to further improve the effects ofthe present invention.

In the ink jet recording method of the present invention, a recordingliquid prepared as described above will be employed, and printing iscarried out by jetting droplets of the recording liquid in accordancewith a conventional method, whereby a printed product of high qualitycan be obtained under good jetting stability.

Now, the present invention will be described in further detail withreference to Examples. However, it should be understood that the presentinvention is by no means restricted to such specific Examples. In thefollowing Examples, “parts” and “%” mean “parts by weight” and “% byweight”, respectively.

EXAMPLE 1

Preparation of Recording Liquid

Composition of recording liquid Amount (parts) Carbon black (A) 4.0 Nasalt of copolymer of 0.4 styrene/acrylamide-2-methylpropane sulfonicacid/(2,4- dihydroxybenzophenone) adduct of glycidyl methacrylate(random polymer: weight ratio of monomers = 30/50/20, weight averagemolecular weight = 6,000) 1,3-Dimethyl-2-imidazolidinone 4.0 Deionizedwater 35.6 Total 44.0

The above-identified components were taken into a cylindrical stainlesssteel container and subjected to dispersion treatment for 40 hours bymeans of a sand grinder together with 67 parts of glass beads having anaverage size of 0.5 mm. To the obtained liquid, 0.1 part of Olfin E1010(acetylene glycol ethylene oxide adduct, HLB: 13, manufactured byShinetsu Chemical Co., Ltd.) and 5 parts of deionized water were addedand thoroughly stirred. Then, 4 parts of glycerol, 3 parts of ethanoland 43.9 parts of deionized water were further added thereto. Thisliquid was filtered under pressure by means of No. 5C filter paper, andthe liquid thereby obtained was used as a recording liquid.

Printing Test

The recording liquid obtained by the method disclosed in the aboveExample, was filled into a black cartridge (HP51629A) for DeskWriter660Cmanufactured by Hewlett Packard, which was preliminarily cleaned, andthe cartridge was set in a printer. A black solid of 5 cm×5 cm wasprepared (100% Duty) on the after-mentioned Mac Draw, and ink jetrecording was carried out on an electrophotographic paper (Xerox 4024paper, manufactured by Xerox Corporation, the pH of the paper was 6.4 asmeasured by a cool water extraction method as disclosed in JIS P8133)under the following conditions.

Printing Conditions

Printer: DeskWriter660C, manufactured by Hewlett Packard

Ink Cartridge: HP51629A

Computer: Macintosh Performa550

Software: Mac Draw II 1.1

Print Option: Monochromatic Printing

Paper Setting Paper Size: A4, Paper: Pulp Paper

Option

Density Setting: Normal,

Ink Control: Automatic,

Half Tone: Automatic,

Color Adjustment: Automatic

Print Quality: Normal (600×300 dpi)

As a result, jetting performance was good and constant without clogging,and a printed product of good printing quality was obtained. The resultsof evaluation by the following methods are shown in Table 1.

Measurement of S.A.D.

The S.A.D. of the solid portion of the printed product obtained by theabove printing test was measured under the following measuringconditions.

Measuring Method

Apparatus: Scanning Probe Microscope

Type of Machine: NanoScope III, manufactured by Digital InstrumentsCompany

Scanner: J-Head

Measured Region: 1 μm×1 μm

Number of Pixels: 512×512

Scan Rate: 1.5 Hz

Measuring Mode: Tapping AFM

Probe: Si-DF 20, manufactured by Seiko Instruments Co., Ltd.

Image Treatment: Planefit Auto tertiary

Under the above conditions, the surface of the printed portion wasmeasured, and the S.A.D. was calculated. The measured regions wereportions other than fiber portions of the paper, and an average of fourpoints (four regions) was taken as the data.

Evaluation of Printing Density

The density of the printed product obtained by the above printing testwas measured by means of a Macbeth reflection densitometer (RD914). Theresults were evaluated under the following standards and shown in Table1.

⊚: OD being at least 1.5

∘: OD being at least 1.4 and less than 1.5

Δ: OD being at least 1.3 and less than 1.4

X: OD being less than 1.3

Water Resistance Test

The printed product obtained in the printing test, was immersed in citywater in a beaker for 5 seconds. The printed product was dried, and thepresence or absence of print smudging was visually evaluated. Theresults were evaluated under the following standards and shown in Table1.

∘: no substantial print smudging observed.

Δ: slight print smudging observed, but practically no problem.

X: substantial print smudging observed.

Light Resistance Test

The printed product was irradiated for 100 hours by means of a xenonfade meter (manufactured by Suga Shikenki K.K.), whereupon discolorationwas visually evaluated. The results were evaluated under the followingstandards and shown in Table 1.

∘: good

Δ: slight discoloration observed, but practically no problem.

X: substantial discoloration observed.

Measurement of Particle Size Distribution

The obtained recording liquid was, at the concentration as it was,subjected to the measurement of the particle size distribution by aparticle size distribution meter (MicrotracUPA, sold by Nikkiso).

Measuring Conditions

Transparent Particles: No, Spherical Particles: No,

Particle Refractive Index: 1.81

Particle Density: 1.86

Fluid Refractive Index: 1.33

High Temp: 30.0° C., Viscosity: 0.797 cP

Low Temp: 20.0° C., Viscosity: 1.002 cP

Run Time: 300 (sec), Number of Runs: 2

An average value of two measurements conducted under the above measuringconditions, was taken as the value of the particle size distribution ofthe recording liquid. As a result, the average particle size of therecording liquid obtained in Example 1 was 0.068 μm.

Storage Stability Test

The obtained recording liquid was stored for one week at 70° C., andafter the storage, it was returned to room temperature and at theconcentration as it was, subjected to the measurement of particle sizedistribution in the same method as described above by a particle sizedistribution meter (MicrotracUPA, sold by Nikkiso). The obtained resultswere compared with the results of the above test of particle sizedistribution, to take differences for the respective fractions of themeasured particle sizes, and the total of the differences (%) wascalculated.

EXAMPLE 2

Preparation of recordiing liquid

Composition of recording liquid Amount (parts) Carbon black (B) 4.0 Nasalt of copolymer of 0.4 styrene/acrylamide-2-methylpropane sulfonicacid/(2,4-hydroxybenzophenone) adduct to glycidyl methacrylate (randompolymer: weight ratio of monomers = 30/50/20, weight average molecularweight = 6,000) 1,3-Dimethyl-2-imidazolidinone 4.0 Deionized water 35.6Total 44.0

The above-identified components were taken into a cylindrical stainlesssteel container and subjected to dispersion treatment for 3 hours bymeans of a sand grinder together with 152 parts of zirconia beads havingan average size of 0.5 mm. To the obtained liquid, 4 parts of glycerol,3 parts of ethanol and 49 parts of deionized water were added andthoroughly stirred. Then, this liquid was filtered under pressure bymeans of No. 5C filter paper, and the liquid thereby obtained was usedas a recording liquid. The average particle size of the obtained liquidwas 0.180 μm. Further, using the recording liquid obtained here,printing and evaluation were carried out in the same manner as inExample 1. The results are shown in Table 1.

EXAMPLE 3

Preparation of Recording Liquid

Composition of recording liquid Amount (parts) Color Black FW18 4.0(manufactured by Degussa) Na salt of copolymer of 0.4styrene/acrylamide-2-methylpropane sulfonic acid/acrylic acid (randompolymer: weight ratio of monomers = 50/30/20, weight average molecularweight = 8,000) 1,3-Dimethyl-2-imidazolidinone 4.0 Deionized water 35.6Total 44.0

The above-identified components were taken into a cylindrical stainlesssteel container and subjected to dispersion treatment for 3 hours bymeans of a sand grinder together with 152 parts of zirconia beads havingan average size of 0.5 mm. To the obtained liquid, 4 parts of glycerol,3 parts of ethanol and 49 parts of deionized water were added andthoroughly stirred. Then, this liquid was filtered under pressure bymeans of No. SC filter paper, and the liquid thereby obtained was usedas a recording liquid. The average particle size of the obtained liquidwas 0.103 μm Further, using the recording liquid obtained here, printingand evaluation were carried out in the same manner as in Example 1. Theresults are shown in Table 1.

Comparative Example 1

The ink of a commercial black ink cartridge for ink jet recording (HPC4840A, manufactured by Hewlett Packard) was withdrawn, and evaluationwas carried out in the same manner as in Example 1. The results areshown in Table 1.

Comparative Example 2

The S.A.D. of Xerox 4024 paper alone was measured and found to be 7.0.From this result, it was confirmed that the values of S.A.D. in Examples1 to 3 and Comparative Example 1, 3, 4 and 5 were values derived fromthe recording liquids.

Comparative Example 3

The ink of a commercial black ink cartridge for ink jet recording (HP51645A, manufactured by Hewlett Packard) was withdrawn, and evaluationwas carried out in the same manner as in Example 1. The results areshown in Table 1.

Comparative Example 4

The ink of a commercial black ink cartridge for ink jet recording (HP51629A, manufactured by Hewlett Packard) was withdrawn, and theevaluation was carried out in the same manner as in Example 1. Theresults are shown in Table 1.

Comparative Example 5

The ink of a commercial black ink cartridge for ink jet recording(12A1970, manufactured b Lexmark Company) was withdrawn, and evaluationwas carried out in the same manner as in Example 1. The results areshown in Table 1.

TABLE 1 Storage Water Light Test Resist- Resist- Printing S.A.D. (%)ance Test ance Test Density Example 1 61.0 9.28 ◯ ◯ ◯ Example 2 68.114.88 ◯ ◯ ⊚ Example 3 61.9 13.20 ◯ ◯ ◯ Comparative 59.2 23.52 ◯ ◯ ΔExample 1 Comparative 43.5 26.50 ◯ ◯ X Example 3 Comparative 43.2 19.04◯ ◯ X Example 4 Comparative 23.6 18.72 ◯ ◯ X Example 5

In Table 1, the storage stability test (%) is the results obtained bytaking differences in the particle size distribution between immediatelyafter the preparation of the recording liquid and after storage for oneweek at 70° C. and calculating the total of the differences.

In the following Table 2, the physical properties of carbon blacks usedin Examples 1 and 2 are shown.

TABLE 2 Specific Particle Surface DBP Oil FC Volatile Size AreaAbsorption or Content (nm) (m²/g) (ml/100 g) pH CC* (wt %) Carbon 15 262147 5.0 FC 1.0 Black A Carbon 14 294 147 7.0 FC 3.0 Black B Color 15 260160 4.0 CC 4.5 Black FW18 *FC: Furnace Carbon Black CC: Channel CarbonBlack

When the recording liquid of the present invention is employed, it ispossible to obtain a stabilized recorded image with a high recordingdensity and free from printing irregularities, even when recorded by inkjet recording on pulp paper or regenerated paper, and the storagestability and jetting stability are good, and further, it is possible toobtain a record which is excellent in fastness of an image, such aswater resistance or light resistance. With such characteristics, therecording liquid of the present invention is useful not only for ink jetrecording or writing but also as a recording liquid for other purposes.

What is claimed is:
 1. A recording liquid comprising an aqueous mediumand a water-insoluble pigment characterized in that when it is printedwith 100% duty and with a resolution of 600×300 dpi on anelectrophotographic paper having a S.A.D. (Surface Area Difference) offrom 6.0 to 9.0 and a pH of from 6 to 8, the S.A.D. of the printedportion is at least 59.5 wherein said electrophotographic papercomprises a rosin-type abeitic acid as a sizing agent and from 1.8 to2.2 wt. % of Ti atoms in said paper.
 2. The recording liquid accordingto claim 1, wherein the S.A.D. of the printed portion is within a rangeof from 60.0 to 90.0.
 3. The recording liquid according to claim 1,wherein the density of the printed portion is at least OD1.5.
 4. Therecording liquid according to claim 1, wherein the water-insolublepigment is carbon black.
 5. The recording liquid according to claim 1,wherein the total of differences between the particle size distributionimmediately after the preparation of the recording liquid and theparticle size distribution after storage of the recording liquid for oneweek at 70° C., is at most 20%.
 6. The recording liquid according toclaim 1, which contains an anionic polymer having anionic water-solublegroups and having a pKa of at most
 3. 7. The recording liquid accordingto claim 1, which contains an anionic polymer having sulfonic orsulfonate groups.
 8. A printed product obtained by an ink jet recordingmethod which comprises jetting droplets of the recording liquid asdefined in claim
 1. 9. An ink jet recording method which comprisesjetting droplets of a recording liquid to carry out recording whereinthe recording liquid as defined in claim 1 is used as the recordingliquid.